Hearth roll for continuous annealing furnaces, and method for manufacturing same

Abstract

A method for manufacturing a hearth roll for continuous annealing furnaces includes a first step of applying an aqueous solution containing chromium phosphate onto a thermal spray coating film formed on the roll surface of a hearth roll or impregnating the thermal spray coating film with the aqueous solution; and a second step of burning the hearth roll.

The invention claimed is: 
     
       1. A method for manufacturing a hearth roll for continuous annealing furnaces, comprising:
 a first step of applying an aqueous solution containing chromium phosphate onto a thermal spray coating film formed on a roll surface of the hearth roll; and 
 a second step of burning the hearth roll, 
 wherein the thermal spray coating film is a CoCrAlY-based cermet thermal spray coating film, and 
 when an amount of the aqueous solution is 100% by mass, a concentration of chromium phosphate is 5% by mass to 30% by mass, and a concentration of chromium in the chromium phosphate is 1.5% by mass to 15% by mass. 
 
     
     
       2. The method for manufacturing a hearth roll for continuous annealing furnaces according to  claim 1 , wherein the burning is performed once in the second step. 
     
     
       3. The method for manufacturing a hearth roll for continuous annealing furnaces according to  claim 1 , further comprising a step of forming the thermal spray coating film on the roll surface of the hearth roll before the first step of applying the aqueous solution containing the chromium phosphate onto the thermal spray coating film,
 wherein in the first step of applying the aqueous solution, the aqueous solution is permeated into pores formed in the thermal spray coating film and is attached to a surface of the thermal spray coating film, 
 in the second step of burning the hearth roll, a burned product containing a metaphosphoric acid, a high polymer and oxides of chromium is generated inside the pores of the thermal spray coating film and on the surface of the thermal spray coating film, and 
 the burned product does not include a hexavalent-chromium. 
 
     
     
       4. The method for manufacturing a hearth roll for continuous annealing furnaces according to  claim 3 , wherein the aqueous solution contains a surfactant, and a concentration of the surfactant is no less than 0.001% and less than 1%. 
     
     
       5. The method for manufacturing a hearth roll for continuous annealing furnaces according to  claim 4 , wherein in the second step of burning the hearth roll, a burning temperature is between 250° C. and 700° C.